Most syringes for hypodermic injection of a liquid into a subject are capable of repeated use if a user so desires, or the syringe can be destroyed by the user so that it cannot be used again.
The need for a hypodermic syringe that cannot be reused has become particularly important in view of the repeated reuse of discarded hypodermic syringes by drug addicts without proper sterilization between each use. Blood born infectious diseases are spread between drug addicts that share a syringe. This has been identified as a major cause of the spread of hepatitis, venereal disease, and AIDS among drug addicts. Drug addicts are known to rummage through the trash of a hospital in an effort to find discarded syringes. Clearly, that source of syringes for illicit use by drug addicts would be stopped if all syringes were destroyed after use and before being discarded.
Heretofore this problem has been addressed time and again in efforts to provide a non-reusable syringe and in all of those efforts attention is paid to the way the drug addict uses the discarded syringe and the effort is made to redesign the syringe so that it cannot be used in that way. The usual illicit use of a hypodermic syringe involves filling the syringe with liquid for injection from an open vessel, which is done by inserting the syringe needle into the liquid and drawing back the syringe piston creating a slight vacuum in the syringe so that liquid from the vessel flows under atmospheric pressure through the needle into the syringe.
A very simple way to frustrate this illicit use it to break of destroy the needle of the syringe or destroy the piston or destroy the cylinder. These "destroy" techniques are not automatic and so the destruction is discretionary with the user. A more subtle technique provides a plunger that can be retracted only once. More particularly, after a first retraction and injection by a legitimate user, the piston cannot be withdrawn again to draw in another charge of liquid for injection, because the stem attached to the piston hits against a stop. Unfortunately, the stop can be tampered with and made ineffective and so the syringe can be used again when that is done.
Thus, while some of the techniques used in the past to provide a non-reusable syringe are automatic and are not discretionary with the first user, they can be tampered with by a drug addict and the syringe used again. The other techniques that destroy useful parts of the syringe are quite effective provided they are carried out and since all are discretionary with the first user, such syringes that come initially into the hands of a drug addict never get destroyed and are passed around and give rise to the problem.
It is an object of the present invention to provide a hypodermic syringe that cannot be used in the conventional way that hypodermic syringes are used by drug addicts, and, in particular, cannot be filled with liquid for an injection from an open vessel.
It is an object of the present invention to provide a hypodermic syringe that does not depend upon a discretionary act of the first user to limit the usefulness of the syringe for illicit use by a drug addict.
It is another object of the present invention to provide a hypodermic syringe that is not reusable by any conventional way that drug addicts use a syringe and where that condition does not depend upon a discretionary action by a first user, and so some of the limitations mentioned above of prior non-reusable syringes are avoided.
It is another object to provide a hypodermic syringe that is intrinsically less useful for illicit uses, because the syringe piston cannot be withdrawn to draw by vacuum a liquid into the syringe, while the syringe can be used repeatedly by those having facilities for loading the syringe with liquid from a pressurized rubber diaphragm vial of the liquid.